Although the first useful lasers were developed in the 1960s, recent advances in laser and fiber optic delivery systems have greatly enhanced the use of this technology in the field of medicine. Today there are numerous types of laser systems designed for operation in a wide range of applications primarily related to surgical and other medical procedures.
A common type of laser known as a CO2 laser delivers radiation with a wavelength of 10.64 microns. However, in order to focus or channel the radiated energy produced by a CO2 laser it is necessary to configure sets of mirrors in certain ways. These systems are typically large and expensive. With the advent of the Nd:YAG type laser delivering electromagnetic energy at a wavelength of 1.064 microns, it became possible to generate and focus the laser radiation through a silica core optical fiber. Thus, fiber optic surgical tools have become important in certain procedures. The range of their utility is still being explored and discovered.
Laser fibers are used in different ways, including incision, necrosis or killing of live tissue, excision or removal of tissue and structure, and cauterization of tissue. During incision and removal of tissue, a beam of laser radiation causes an instantaneous vaporization of the water molecules in the tissue contacted by the beam. The tissue seems to disappear with a puff of steam, leaving behind a very small amount of charred tissue. This process is called ablation, or more specifically photoablation, a term which refers to the removal of live, diseased or dead tissue by vaporization. Incision is accomplished using a very narrow beam directed to a small point drawn across the tissue being incised. A very focused beam would provide the greatest amount of control during either operation.
Cauterization and necrosis of living tissue is accomplished by coagulation, or more precisely with respect to the laser itself, by photocoagulation of contacted or penetrated tissue. In this process the laser beam causes the proteins in the contacted tissue to heat up rapidly and thermally denature. This essentially kills living tissue and seals blood vessels. The process has been likened to frying an egg. In practice, during an incision procedure cauterization of the incised tissue is likely to occur simultaneously. Thus, laser surgery is often characterized by an absence of bleeding during the surgery.
The protocol for a given procedure might specify the type of fiber tip, rate and mode of power delivery, time parameters, etc. Typically, although light at 10.64 is strongly absorbed by the H2O molecule resulting in efficient incision or ablation of soft tissue, a surgeon may be able to defocus the radiation from a CO2 laser and cause a scattering of radiation, with a resulting effect of cauterization. This is the effect of YAG-type laser energy. Since light at 1.064 microns is not strongly absorbed by water molecules the radiant energy scatters or is dissipated throughout the tissue, at and below the surface, and overall coagulation occurs. However, when used in conjunction with a fiber optic surgical tool, the Nd:YAG laser is capable of creating a very narrow beam, thereby making possible incision and ablation as well as cauterization and. coagulation.
In the prior art there are described devices which generate a dual wavelength beam of radiation and are thereby capable of both cutting and cauterizing. Such devices generally use one type of laser with some type of harmonic generator for providing half or double fundamental wavelength beams. There also exist inventions which deliver energy at much shorter wavelengths, such as 250-350 nm. At these wavelengths proteins, as opposed to water molecules, absorb the radiation. These systems, however, are less suitable for general types of surgical operations since they are more complicated to operate. Use of such systems has not become standard in most medical facilities and their cost is generally too high to justify their purchase for occasional use in fairly specialized procedures.
The construction of optical fibers used in surgical procedures is fairly simple. A plastic or silicone cladding is often used to protect the quartz fiber which itself transmits the laser radiation. These types of fibers are termed "multi-mode" fibers and the beam of photons entering the fiber are all travelling in roughly the same direction. Theoretically, only a few of the entering photons are directed straight down the axis of the fiber. Transmission of the radiant beam is possible since the rest of the photons are constrained to the core of the fiber due to internal reflectance, generally by the outer surface of the fiber or the inner surface of the cladding. Very few photons escape the fiber. The technology related to the use of silica core fibers in medical lasers is well known, e.g. B. P. McCann, Photonics Spectra, May 1990, pp 127-136.
Differences between these types of optical fibers and those used in telecommunications and data transmission are important. Several design factors must be considered such as sterilizability, quartz core integrity and purity, power capacity and index of refraction of materials of construction.
Generally, 20 to 100 watts of energy are used to perform soft tissue surgery. A scalpel used externally might be operated much differently than a scalpel used in internal or endoscopic surgery. Scalpels used with most types of endoscopes are very small. Additionally, often laser surgery is performed with irrigation by a cooling gas or liquid to cool the scalpel firing tip as well as to prevent the tissue from overheating. Some endoscopes have multiple channels to accommodate a viewing port or camera, a laser delivery device, and an irrigation supply and accompanying vacuum channel.
Delivery of high power radiation can have a very damaging effect on the scalpel tip itself. One of the problems with existing designs is that the tip which directs the laser beam to a right angle becomes overheated. This is caused by an absorption of power (heat) at the reflecting surface. Overheating of the firing tip can be caused by an accumulation of incompletely burned tissue which rapidly heats up. Fouling of the firing tip can trigger a process known as thermal runaway. As heat builds up, the firing tip gets hot and sometimes starts to melt or deform. Often, angle firing surgical scalpels will need to be replaced partway through the surgical operation due to this problem.
One solution to firing tip overheating is to provide a transparent, hard, heat resistant tip, such as sapphire or quartz. An alternative is to provide a highly reflective surface in the scalpel tip for deflecting the beam. This invention discloses a device with a reflecting coating deposited or otherwise applied to the transmitting end or firing tip of an optical fiber waveguide such that the beam of radiation is internally reflected out one side of the transmitting end of the waveguide. The invention comprises an internally reflected source of cutting power which could be used in a variety of cutting or heating applications calling for power delivery at an angle to the power source.
One material capable of being deposited in a very thin coating and producing a very high reflectance is gold. A protective layer over the reflective material could also be applied and be useful to add durability and thermal resistance to the reflective material. U.S. Pat. No. 4,992,087, incorporated herein by reference, discloses a reflective coating consisting of a metal or metal alloy and a process for applying it to a glass surface.
Multiple layer optical interference films, also known as interference filters, are well known in the art. Such films comprise alternating layers of two or more materials, typically one with a relatively high index of refraction and the other with a relatively low index of refraction. These materials are also known as dielectrics. Such are well known in the art and can be designed to reflect or transmit light radiation from various portions of the electromagnetic spectrum. Often, materials with high and low indexes of refractivity are applied in alternating layers so as to comprise a "quarter wave stack", each layer having a thickness equal to approximately one quarter wavelength of the incident light wave. These types of reflectors have been described providing optical absorption losses of as little as 0.0001% to 0.0002%.
Methods for manufacturing these films are described in the prior art. U.S. Pat. No. 4,925,259, incorporated herein by reference, describes a damage-resistant dielectric coating formed over a silica substrate. Using a pulsed-plasma assisted chemical vapor deposition process several hundreds and even thousands of layer pairs can be deposited rapidly. Larger differences between the indices of refraction require a lesser number of layer pairs to obtain a given value of reflectance. In some cases, the indices of refractivity of alternating materials can be very similar and the number of layers very great. These coatings seem to have superior damage-resistance to optical radiation, approaching the damage resistance of pure silica. For laser applications using high power, components can be made to withstand high energy flux densities. They are also resistant to abrasion. Since the materials are very similar in composition there are fewer problems associated with differences in thermal and mechanical properties. Peeling and scaling is avoided as are microcracks which, in a given layer, would otherwise occlude the film.
At the reflecting surface, if most of the incident radiation is reflected very little will be absorbed and the temperature at the surface will not rise significantly, especially using today's advanced lasers with pulsed energy, high-peak pulsing and temperature detecting fiber tip protection systems. In the prior art, providing such a reflective coating such as an interference film to internally reflect the beam of a laser used in conjunction with an optical fiber to perform surgical or other cutting or heating procedures is unknown.
Another problem associated with current laser scalpels is that they are often clumsy to use and difficult to manipulate precisely. One problem is that the quartz fiber is so thin it is difficult to grasp effectively, especially if it is used in conjunction with a cystoscope or some type of endoscope where the firing end cannot be controlled directly by the surgeon. Also, as the scalpel is rotated and manipulated by the surgeon, the fiber becomes twisted under a certain amount of angular torque. It would be desirable to provide a scalpel which would be easily controlled, perhaps through the use of some external gripping apparatus attached to the optical waveguide.
Many surgical operations are standard and the procedures followed are routine and well known in the field. For example, in prostate surgery to reduce an enlarged prostate, a typical surgical procedure using a laser scalpel would be to fire energy at four specific anatomic zones causing ablation in very precisely delimited areas in the prostate gland itself. Since the four points procedure is common it would be desirable to provide the surgeon with a scalpel which would select consecutively and precisely the exact points of laser beam contact, making the operation safer and less prone to surgeon error.
The following describes the method for performing a prostatectomy, the removal of tissue from an enlarged prostate gland. Using a laser scalpel, the tissue to be removed is coagulated to kill the tissue, perhaps at the four-points referred to above. Typically this might result in an immediate swelling of the surrounding tissue. Therefore, a catheter would be allowed to remain in place for several days following the operation to allow for drainage of urine. Once the swelling subsides the catheter would be removed and over a period of several weeks the dead tissue would slough off naturally. It would be desirable to provide a scalpel which would allow the surgeon to remove the swollen, coagulated tissue in a subsequent vaporization step during the same operation to avoid the need for the catheter completely. As discussed above, radiation at 1.064 microns is not readily absorbed by water molecules. It appears that the high-peak power output type of laser controller is capable of generating higher temperatures useful for vaporization at the surface.
It would be desirable to have an angle firing scalpel which would not overheat and lose integrity and efficiency. It would also be desirable to have an angle firing scalpel which could both cut tissue and perform the cauterization process, either simultaneously or by the surgeon's control. Such a scalpel should be appropriately sized to be convenient to use. It is believed that the present invention meets these needs.